The present invention generally relates to low power devices and more particularly to low power devices performing transactions with smartcards.
Smart cards are plastic cards having an embedded smartcard chip. A smartcard chip is an integrated microcontroller generally comprising a central processing unit, a random access memory, a ROM memory and an EEPROM memory. The smartcard is provided with a contact communication interface. Such a smartcard can carry out a transaction through its contact interface when it is hosted in a smartcard reader. Smart cards are widely used to store sensitive information such as cryptographic keys or software routines that implement valuable algorithms or know-how. Smartcards are notably used for authentication purposes in relation with communication modems.
An increasing number of communication modems are used in environments where their power supply is limited. The use of such modems is notably known for a communication between an energy provider and the consumption counter located at the home of a final user. Such modems can notably be linked to a sensor measuring the electric power consumption, a gas flow or a water flow. On a regular basis, the modem sends the amount measured by the sensor to the energy provider.
Such a modem can be led to work during a significant time or permanently without any external power supply. The modem may notably be left months or years without any external intervention. The operation of such a modem then relies on a battery power supply. If the battery is not charged frequently enough or if it is not timely replaced, the modem may have to power itself off. The modem is then unable to communicate with remote premises. To delay the necessity to proceed to a power off, modems and smartcards need to be provided with efficient low consuming modes.
As the remote communications of the modem are timely spaced (for instance several minutes, hours or days), the modem and the smartcard remain idle most of the time. To benefit from the idle periods, such a modem can be provided with a low power mode. Its static power consumption is thereby reduced during the idle periods in order to increase its autonomy.
When the modem enters in low power mode, it performs a standby process. During the standby process, the modem stops sending APDUs to the smartcard. The smartcard then enters in standby mode. The modem then stops the clock sent to the smartcard. The smartcard then switches from the standby mode to a clock stop mode.
The clock stop mode is the mode where the smartcard has the lowest consumption. Most of the power consumption in clock stop mode is due to leakage currents. Unfortunately, security requirements induce a significant leakage current in conventional smartcards. The smartcards providing the lowest clock stop mode consumption still face a leakage current superior to 50 Microamperes. Thus, even if very efficient modems are used (for instance providing a leakage current as low as several hundreds of nanoamperes), the modem will have to power the smartcard which has a significantly higher power consumption. The smartcard in clock stop mode thus seriously reduces the modem autonomy. The modem and smartcard can thus reveal inappropriate for many applications due to their low autonomy.
An alternative could be to suppress the smartcard power supply when entering into low power mode. In this case when the modem switches back to active mode, the smartcard is powered up. During its start, the smartcard has to load applications and has to communicate with the modem, for instance to send an ATR (Answer to Reset) to modem or to define a PPS (Protocol and Parameter Select) value for the future communications. This solution has two drawbacks:                This protocol is not compliant with ETSI standard, and requires software modifications of the modem.        Starting the smartcard is a quite lengthy process. Each modem remote communication would be delayed by this starting process.        